The development of fiber optic switches has been a result of a need to avoid electrical power in the control lines and switches which can cause explosions in an explosive atmosphere and fatal shocks if in the presence of liquid.
U.S. Pat. No. 3,999,074, issued to Callaghan, discloses the general arrangement of utilizing light transmission to produce a variable electrical output signal to control an electronic switch which, in turn, controls power to a load.
U.S. Pat. No. 4,045,667, issued to Hanson, discloses a single fiber optical control system utilizing a fiber optic bundle to carry light from a transceiver to an optical selector via a fiber optic bundle. The light in the optical receiver is reflected back down the fiber optic bundle to the transceiver where it impinges on one of several photo-detectors depending upon the switch position. The photo-detectors distinguish the spectrum of coloured light to generate multiple electronic control states.
U.S. Pat. No. 4,315,147, issued to Harmer, discloses a two-position switch which has an active actuator that intercepts light passing from one segment of an optical fiber to another when the actuator is depressed and which permits such transmission when the actuator is in an extended position. Because of the need to insert the actuator between the fiber segments, there is a gap between the fiber segments which light must traverse in going from one segment to the other.
U.S. Pat. No. 4,904,044, issued to Tamulevich, discloses a flexible filter oriented between two optical fibers where it serves to filter light passing from one to the other. Again, the filter is spaced apart from each of the two fibers. Moreover, alignment of the two fibers is critical.
U.S. Pat. No. 5,046,806, issued to Kidder et al., in FIGS. 7 and 8 discloses a flexible filter attached on a carrier. Filters are positionable in front of a fiber by movement of a switch body. Again, a lens and a retro-reflector are used after the filter in order to focus and reflect the light back down the fiber.
U.S. Pat. No. 4,704,656 issued to Neiger discloses a single fiber control system using a mirror to reflect light received from a fiber back into the fiber when in a reflecting position. Upon moving the mirror into a non-reflecting position, light from the fiber is not reflected back into the fiber. The mirror is attached to the actuator which swings it in and out of position with respect to the fiber tip. The efficiency of the system is very sensitive to parallelism errors between the fiber face and mirror surface.
In any mirror actuator, the coupling efficiency of the reflected light and, therefore, the effectiveness of the signal detection is sensitive to alignment problems. The mirror actuator mechanism must locate the mirror surface parallel and in very close proximity to the fiber face in order to maintain good efficiency. In any system in which there is a gap between an end of the fiber and the mirror, the surfaces of the fiber and mirror will be prone to contamination. Both back scattering and contamination in such systems will cause loss of light and, hence reduced efficiency.